The present invention relates to a valve drive mechanism that has a rocker arm.
A valve drive, especially for an internal combustion engine of a manually guided implement, has a rocker arm that by means of a swivel joint is movable about a pivot axis that extends transverse to the rocker arm, and that is held on the cylinder head of the internal combustion engine. A control unit that acts upon one end of the rocker arm electromechanically, mechanically or in some other suitable manner, serves for the actuation of the poppet valve. For this purpose, the other end of the rocker arm acts upon the end of the valve stem of the poppet valve.
DE 198 45 489 A1 discloses a valve drive having a rocker arm, according to which flat portions are bent out of the side wall of the rocker arm for the lateral guidance of the rocker arm on the valve stem end of the poppet valve. These portions are cut out of the rocker arm and are bent about 180xc2x0 and project from the rocker arm in the direction of the valve. Such a construction weakens the rocker arm in the region of that end that actuates the valve stem, as a consequence of which the rocker arm is susceptible to fatigue failure. A further drawback of this known valve drive is that the geometry of the rocker arm thereof must be coordinated to the end of the valve stem.
It is an object of the present invention to provide a valve drive mechanism that while providing a rigid, straightforward rocker arm configuration, ensures a reliable lateral guidance between the rocker arm and the end of the valve stem of the poppet valve.